[CentOS] another bizarre thing...

[Fred Smith]

On Tue, Aug 06, 2019 at 05:27:54AM -0600, Warren Young wrote:
> On Aug 5, 2019, at 6:57 PM, Fred Smith <fredex at fcshome.stoneham.ma.us> wrote:
> > 
> > no core file (yes, ulimit is configured)

yeah, I meant "ulimit -c unlimited" is in effect.


I had no idea systemd had made such a drastic change. or is it that
someone at RH decided to make it (nearly) impossible to do? I fail
to see how it is beneficial to anyone to make it so hard to get
core dump files.

but thanks for the details!

Fred
> 
> That’s nowhere near sufficient.  To restore classic core file dumps on CentOS 7, you must:
> 
> 1. Remove Red Hat’s ABRT system, which wants to catch all of this and handle it directly.  Say something like “sudo yum remove abrt*”
> 
> 
> 2. Override the default sysctl telling where core dumps land by writing this file, /etc/sysctl.d/10-core.conf:
> 
>     kernel.core_pattern = /tmp/core-%e-%p
>     kernel.core_uses_pid = 1
>     fs.suid_dumpable = 2
> 
> Then apply those settings with “sudo sysctl —system”.
> 
> I don’t remember what the default is, which this overrides, but I definitely didn’t want it.
> 
> You can choose any pattern you like, just remember what permissions the service runs under, because that’s the permission needed by the process that actually dumps the core to make the file hit the disk.  That’s why I chose /tmp in this example: anyone can write there.
> 
> 
> 3. Raise the limits by writing the following to /etc/security/limits.d/10-core.conf:
> 
>     * hard core unlimited
>     * soft core unlimited
> 
> If this is what you meant by “ulimit,” then great, but I suspect you actually meant “ulimit -c unlimited”, but I believe until you do the above, the ulimit CLI app can have no effect.  You have to log out and back in to make this take effect.
> 
> Once the above is done, “ulimit -c unlimited” can take effect, but it’s of no value at all in conjunction with systemd services, for example, since those don’t run under a standard shell, so your .bash_profile and such aren’t even exec’d.
> 
> 
> 4. If your program is launched via systemd, then you must edit /etc/systemd/system.conf and set
> 
>     DefaultLimitCORE=infinity
> 
> then say “sudo systemctl daemon-reeexec”
> 
> Case matters; “Core” won’t work.  Ask me how I know. :)
> 
> 
> 5. If you have a systemd unit file for your service, you have to set a related value in there as well:
> 
>     LimitCore=infinity
> 
> You need both because #4 sets the system-wide cap, while this sets the per-service value, which can go no higher than the system cap.
> 
> 
> 6. Restart the service to apply the above two changes.
> 
> 
> Yes, it really is that difficult to enable classic core dumps on CentOS 7.  You’re welcome. :)
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-- 
---- Fred Smith -- fredex at fcshome.stoneham.ma.us -----------------------------
  "For him who is able to keep you from falling and to present you before his 
 glorious presence without fault and with great joy--to the only God our Savior
 be glory, majesty, power and authority, through Jesus Christ our Lord, before
                     all ages, now and forevermore! Amen."
----------------------------- Jude 1:24,25 (niv) -----------------------------